As one example of semiconductor manufacturing, there is available a vertical heat treatment apparatus for thermally treating, e.g., a plurality of semiconductor wafers (hereinafter referred to as wafers) in a batch-wise manner. The vertical heat treatment apparatus is installed in an air atmosphere. The vertical heat treatment apparatus includes a carrier conveying region in which a wafer-holding carrier called a FOUP is conveyed. The vertical heat treatment apparatus also includes a wafer conveying region in which wafers are transferred to a wafer boat as a substrate holding mechanism and are conveyed to a heat treatment furnace. A partition wall is formed between the carrier conveying region and the wafer conveying region. In order to maintain the cleanliness of the wafer conveying region higher than that of the carrier conveying region and to prevent generation of natural oxide films on the wafers, the atmosphere of the wafer conveying region is converted from the air to nitrogen, thereby keeping the oxygen concentration low. It is sometimes required that the oxygen concentration be reduced to, e.g., several ppm or less.
A conveying gateway for the wafers is formed in the partition wall. The conveying gateway is opened and closed by an opening/closing door conforming to a FIMS (Front-Opening Interface Mechanical Standard). The opening/closing door is provided with a removal mechanism for removing a lid installed on the front surface of a carrier. In other words, the opening/closing door is required to open and close the lid to transfer the wafers between the inside of the carrier and the wafer conveying region, and to isolate the wafer conveying region from the carrier conveying region to keep the wafer conveying region at a low oxygen concentration.
The lid removing process will be described in more detail. In a state where the front surface of the carrier remains in contact with the partition wall, the removal mechanism acts on an engaging mechanism installed within the internal space of the lid and arranged to bring the lid into engagement with the carrier, thereby releasing the engagement. Then the opening/closing door and the lid removal mechanism are moved toward the wafer conveying region in a state where the released lid is held by the lid removal mechanism, whereby the inside of the carrier is opened to the wafer conveying region. When the opening/closing door is moved in this manner, the air staying within the internal space is leaked to the wafer conveying region. Consequently, the nitrogen concentration in the wafer conveying region is reduced and the oxygen concentration in the wafer conveying region is increased. As a result, it may become impossible to subject the wafers to a desired treatment.